Sample A Case Study By Dan Krane DanKraneWrightedu Carrie Rowland RowlandBioforensicscom Nathan Adams AdamsBioforensicscom Financial disclosure Employees of Forensic ID: 702686
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Slide1
Disputed DNA Stats for a Low-level Sample:A Case Study
By
Dan
Krane
–
Dan.Krane@Wright.edu
Carrie Rowland –
Rowland@Bioforensics.com
Nathan Adams –
Adams@Bioforensics.comSlide2
Financial disclosureEmployees of Forensic Bioinformatic Services, Inc.Slide3
Case factsAlleged sexual assaultSample from underwear1 nanogram amplified, using
Identifiler
® (15 autosomal loci)
Victim apparent major profile
“Minimal”
minor profileSlide4
Vic
Sus
Major
Minor
D8
13, 16
16, 16
13,
16
-
D21
27, 29
29, 33.2
27,
29
-
D7
11, 11
11, 12
11, 11
-
CSF
10, 11
9, 9
10, 11
-
D3
15, 18
15, 17
15,
18
-
THO1
8, 9
6, 9.3
8, 9
6, 9.3
D13
10, 13
11, 11
10, 13
11
D16
13, 13
12, 13
13, 13
-
D2
18, 21
19, 23
18, 21
19
D19
13, 14
12, 16
13, 14
-
vWA
15, 17
14, 19
15, 17
-
TPOX
9, 10
10, 12
9,
10
-
D18
16, 16
14, 18
16, 16
14
Amel
X, X
X, Y
X, X
X,
Y
D5
11, 12
10, 10
11, 12
-
FGA
24, 25
23, 26
24, 25
-Slide5
“Minimal” minor
Vic
Sus
Major
Minor
THO1
8, 9
6, 9.3
8, 9
6, 9.3
D13
10, 13
11, 11
10, 13
11
D2
18, 21
19, 23
18, 21
19
D18
16, 16
14, 18
16, 16
14Slide6
“Minimal” minor5 alleles at 4 loci“1 or more than 1 contributors”1 in 220 unrelated individualsSlide7
Calculated locus stats
Minor
THO1
0.633
D13
0.524
D2
0.059
D18
0.231
Total
0.0045
Or 1-in-220 unrelated individuals
*
*
*
=Slide8
Points of contentionDropout + no assumed number of minor contributorsNomenclatureLab claimed to have “modified” the Random Match Probability (
RMP)Slide9
“Minimal” minor
Minor
THO1
6, 9.3
D13
11
D2
19
D18
14Slide10
TH01 – 6, 9.3
Allele
Profiles
6
6,6
9.3
6, all but 6
9.3,9.3
9.3,
all but
9.3
-
6,9.3
Locus Freq.0.633Slide11
D13 - 11
Allele
Profiles
11
11, 11
11,
all but
11
Locus Freq.
0.524Slide12
D2 - 19
Allele
Profiles
19
19, 19
19,
all but
19
Locus Freq.
0.059Slide13
D18 - 14
Allele
Profiles
14
14, 14
14,
all but
14
Locus Freq.
0.231Slide14
“Minimal” minor
Minor
THO1
6, 9.3
[6, 6] [9.3, 9.3]
[6,
9.3]
[6, _]
[9.3, _]
D13
11
[11, 11] [11,
_]
D219[19, 19] [19, _]
D18
14
[14, 14] [14, _]Slide15
Contributors accountedfor by reported stat
Minor
A
B
THO1
6, 9.3
6, _
9.3, _
D13
11
11, _
11, _
D2
19
19, _
19, _
D18
14
14, _
14, _Slide16
Lab stat vs.SWGDAM modified RMPDefense: “… SWGDAM
specifically says
… you
could
only use a modified RMP when you actually
assume
a
particular number
of contributors, right
?”
Lab: “They actually say the unrestricted. They don't use the term ‘modified’, so we're modifying it.”Slide17
SWGDAM – modified RMP4. Statistical Analysis of DNA Typing Results “…this document also applies the term RMP to mixture calculations where the number of contributors is assumed (this has sometimes been referred to as a
‘
modified RMP’).”Slide18
Modified Random Match Probability (mRMP)“By definition, the RMP is calculated on a single-source profile, so for a mixture sample, … this approach is often called a ‘modified’ RMP (mRMP
).” (Butler
2014)Slide19
“By using the RMP nomenclature, these calculations are distinguished from the CPI nomenclature which is commonly thought of in terms of a mixture calculation that makes no assumption as to the number of contributors.”SWGDAM – RMP vs. CPISlide20
Lab statDefense: “But didn't the ultimate number you came up with assume that it was all from the same person?”
Lab: “No
, it did not
.”Slide21
What the lab said“…statistically I'm taking into account any dropout that could possibly be occurring instead of saying that all those
alleles are
there and it's that one
person
…” [emphasis added]Slide22
What the calculations sayAt the TH01 locus, a contributor must have a 6 or a 9.3At the other three loci, a contributor must have the observed alleleReported cumulative productSlide23
What this means“statistically I’m taking into account any dropout that could possibly be occurring” … as long as the dropout is always for alleles we didn’t see and the contributor(s) otherwise
match the observed “minimal” minor profile at one allele per locus.Slide24
Contributors accountedfor by reported stat
Minor
A
B
THO1
6, 9.3
6, _
9.3, _
D13
11
11, _
11, _
D2
19
19, _
19, _
D18
14
14, _
14, _Slide25
What if we allow for locus dropout?Slide26
ContributorsNOT accountedfor by reported stat
Minor
A
B
THO1
6, 9.3
6, _
9.3, _
D13
11
_, _
11, _
D2
19
19, _
_, _
D18
14
14, _
14, _Slide27
ContributorsNOT accountedfor by reported stat
Minor
A
B
C
THO1
6, 9.3
6, _
_, _
9.3, _
D13
11
_, _
11, _
_,
_
D2
19
19, _
_, _
_
, _
D18
14
14, _
14, _
_, _Slide28
“modification of” RMPLab: “…what our laboratory uses is a
modification
of an unrestricted
random match probability.”
Defense: “And
is it modified because
you're
applying it to
unknown numbers
of contributors
?”
Lab: “Yes
, that's correct
.”Defense: “Very good.”Lab: “And it allows for dropout.”Slide29
“modification of” RMPLab: “We've been using the same statistical calculations since we started PCR STR testing 15 years ago.”Slide30
Daubert decision“…such a formula appears wholly contradictory to the only portion of the [SWGDAM] Guidelines that sound non-permissive.”Slide31
Daubert decision“The formula [Lab] used did not rely on a conclusive determination whether allelic dropout had occurred or on a specific number of contributors, making its probability statistic misleading at best.”Slide32
Daubert decision“Even if this Court were to determine that [Lab]’s formula, its application in this case, and the resulting statistical conclusion were reliable, the evidence fails the M.R.E. 403 balancing test. The probative value is minimal.”Slide33
Daubert decision“…the probative value is outweighed by the danger of unfair prejudice, misleading the panel members, and waste of time.”Slide34
ReferencesSWGDAM (2010) Interpretation Guidelines for Autosomal STR Typing by Forensic DNA LaboratoriesButler, J. M. (2014). Advanced topics in forensic DNA typing: interpretation
. Academic
Press.
Appendix 4, “Worked Mixture Example” by Michael CobleSlide35
Disputed DNA Stats for a Low-level Sample:A Case Study
By
Dan
Krane
–
Dan.Krane@Wright.edu
Carrie Rowland –
Rowland@Bioforensics.com
Nathan Adams –
Adams@Bioforensics.com
Available at –
www.bioforensics.comSlide36
Important notes> 12:1 mixtureStutter threshold applied per SOPsEvidence tested before referencesReferences tested before stats